In-Body Subnetworks (IBS) present a promising platform for delivering eXtended Reality (XR) services, provided that intelligent scheduling mechanisms are employed to mitigate potential interference—particularly when IBS operate as an underlay to 5G and beyond cellular networks supporting enhanced Mobile Broadband (eMBB) users. This paper addresses the coexistence challenge between eMBB and IBS users by proposing a novel downlink transmission framework that leverages beam-domain information to enable efficient spatial resource reuse. The framework aims to meet the stringent delay and reliability requirements of XR users while improving the experienced throughput of eMBB users. Simulation results demonstrate that the proposed spatial reuse algorithm can enhance eMBB throughput by up to 50%, without reducing the number of supported XR users.

In-body Subnetworks (IBS) are set to become key enablers for standalone eXtended Reality (XR) applications, allowing users to leverage smartphones and XR display devices (XRDD) to create immersive virtual and augmented environments. However, supporting reliable XR services over IBS poses significant challenges due to dense deployment, resource constraints, and stringent communication requirements. To address these challenges, we propose a resource allocation algorithm specifically designed for transmitting XR video frames over IBS. We formulate the problem as a reliability maximization task, modeled as a Partially Observable Markov Decision Process (POMDP). A discrete version of the Soft Actor-Critic (SAC) algorithm is employed to derive a near-optimal policy for joint power control and sub-band allocation. Our approach utilizes a multi-agent framework, where each IBS acts as an agent responsible for resource allocation decisions. Our results demonstrate that, despite relying on partial information of the network, the proposed algorithm surpasses distributed benchmark and performs comparable to centralized algorithms, achieving satisfaction rates of 55% and 98% for the case of 8000 IBSs per square kilometer and packet success rate (PSR) thresholds of 99% and 95%, respectively.

In-body subnetworks (IBS) are envisioned to support reliable wireless connectivity for emerging applications including extended reality (XR) in the human body. As the deployment of in-body sub-networks is uncontrollable by nature, the dynamic radio resource allocation scheme in place becomes of the uttermost importance for the performance of the in-body sub-networks. This paper provides a comparative study on the performance of the state-of-the-art interference-aware sub-band allocation algorithms in in-body sub-networks supporting the XR applications. The study identified suitable models for characterizing in-body sub-networks which are used in a snapshot-based simulation framework to perform a comprehensive evaluation of the performance of state-of-art sub-band allocation algorithms, including greedy selection, sequential greedy selection (SG), centralized graph coloring (CGC), and sequential iterative sub-band allocation (SISA). The study shows that for XR requirements, the SISA and SG algorithms can support IBS densities up to 75% higher than CGC.

Swarm production robots, an enabler for Industry 4.0, are expected to establish direct communication links with each other based on proximity. The 3rdGeneration Partnership Project (3GPP)'s New Radio sidelink is a candidate technology to enable such communication links. However, when operating in autonomous resource selection mode (mode 2), sidelink communications are prone to half-duplex and interference problems, the severity of which increases with the swarm's density. In this paper, we study how beam selection using directional antennas and context information can help reduce the impact of these problems and thus improve the reliability of packet reception. We evaluate the effect of directional antennas when applied at the transmitter and receiver, both separately and simultaneously, for increasing swarm density. Our evaluations show that these enhancements let mode 2 achieve 120% more user equipments (UE) in the swarm for a 99.99% reliability target, compared to the case where these enhancements are not applied.

Decentralized cooperative resource allocation schemes for robotic swarms represents an alternative to infrastructure-based communications across different commercial, industrial and environmental protection use cases. The cooperative communication schemes, device sequential and group scheduling in [1], have shown superior performance in comparison to 5G NR sidelink mode 2, but have also shown performance issues due to signaling overhead and signaling induced failures. In this paper we introduce different techniques that reduce the failure probability of data packet transmissions and the packet inter-reception (PIR) time. We evaluate two techniques, respectively, of incremental redundancy using hybrid automatic repeat request and link adaptation by aggregation, as well as their combination for our decentralized cooperative resource allocation schemes and sidelink mode 2. Our results show that the introduced enhancements, allow to double the amount of supported swarm members while achieving four nines reliability when compared to the case where the same enhancements are applied to the sidelink mode 2.

Robotic swarms are becoming relevant across different industries. In an indoor factory, collective perception of the environment can be used for increased factory automatization. It requires reliable, high throughput and low latency communication of broadcasted video data among robots within proximity. We introduce two new decentralized resource allocation schemes that meet these stringent requirements. The two proposed decentralized schemes are denoted as: (i) device sequential, where robots take turns to allocate resources, and (ii) group scheduling, where robots select local group leaders who perform the resource allocation. A comparative evaluation is performed by simulation against a centralized resource allocation scheme and the current 3GPP release 16 NR sidelink mode 2 scheme. Our results show that the two proposed decentralized resource allocation schemes outperform sidelink mode 2 due to the mitigation of the half-duplex problem. The proposed schemes reach the throughput target of 10 Mbps with a reliability of 99.99% for a swarm size of 50 robots.

The requirement to accommodate ultra-reliable low latency communication (URLLC) is one of the most attractive, yet challenging, new features of upcoming 5G systems. A common way to achieve reliability is retransmission; however, the applicability of this mechanism is hindered by the strict latency requirements. Furthermore, the bandwidth is often limited and shared by multiple connections, which may put the packet into a retransmission queue, leading to even larger latency. We address this problem in an uplink setting by introducing the concept of non-orthogonal multiple access hybrid automatic repeat request (NOMA-HARQ). In essence, NOMA-HARQ allows newly incoming packets to share non-orthogonally the same resource with retransmitted packets. The reliability guarantees are preserved by designing a power optimization procedure that takes into account past transmission attempts as well as the time remaining until the deadline.

We present a connection establishment protocol with integrated authentication, suited for Massive Machine-Type Communications (mMTC). The protocol is contention-based and its main feature is that a device contends with a unique signature that also enables the authentication of the device towards the network. The signatures are inspired by Bloom filters and are created based on the output of the MILENAGE authentication and encryption algorithm set, which is used in the authentication and security procedures in the LTE protocol family. We show that our method utilizes the system resources more efficiently, achieves lower latency of connection establishment for Poisson arrivals and allows a 87% signalling overhead reduction. An important conclusion is that the mMTC traffic benefits profoundly from integration of security features into the connection establishment/access protocols, instead of addressing them post-hoc, which has been a common practice.

We present a random access method inspired on Bloom filters that is suited for Machine-Type Communications (MTC). Each accessing device sends a signature during the contention process. A signature is constructed using the Bloom filtering method and contains information on the device identity and the connection establishment cause. We instantiate the proposed method over the current LTE-A access protocol. However, the method is applicable to a more general class of random access protocols that use preambles or other reservation sequences, as expected to be the case in 5G systems. We show that our method utilizes the system resources more efficiently and achieves significantly lower connection establishment latency in case of synchronous arrivals, compared to the variant of the LTE-A access protocol that is optimized for MTC traffic. A dividend of the proposed method is that it allows the base station (BS) to acquire the device identity and the connection establishment cause already in the initial phase of the connection establishment, thereby enabling their differentiated treatment by the BS.

While LTE has been widely rolled out for human-type services, it is also a promising solution for cost-efficient connectivity of the smart grid monitoring equipment. This is a type of machine-to-machine (M2M) traffic that consists mainly of sporadic uplink transmissions. In such a setting, the amount of traffic that can be served in a cell is not constrained by the data capacity, but rather by the signaling constraints in the random access channel and control channel. In this paper, we explore these limitations using a detailed simulation of the LTE access reservation protocol (ARP). We find that 1) assigning more random access opportunities may actually worsen performance and 2) the additional signaling that follows the ARP has very large impact on the capacity in terms of the number of supported devices; we observed a reduction in the capacity by almost a factor of 3. This suggests that a lightweight access method, with a reduced number of signaling messages, needs to be considered in standardization for M2M applications. Additionally we propose a tractable analytical model to calculate the outage that can be rapidly implemented and evaluated. The model accounts for the features of the random access, control channel, and uplink and downlink data channels, as well as retransmissions.

A canonical scenario in Machine-Type Communications (MTC) is the one featuring a large number of devices, each of them with sporadic traffic. Hence, the number of served devices in a single LTE cell is not determined by the available aggregate rate, but rather by the limitations of the LTE access reservation protocol. Specifically, the limited number of contention preambles and the limited amount of uplink grants per random access response are crucial to consider when dimensioning LTE networks for MTC. We propose a low-complexity model of LTE's access reservation protocol that encompasses these two limitations and allows us to evaluate the outage probability at click-speed. The model is based chiefly on closed-form expressions, except for the part with the feedback impact of retransmissions, which is determined by solving a fixed point equation. Our model overcomes the incompleteness of the existing models that are focusing solely on the preamble collisions. A comparison with the simulated LTE access reservation procedure that follows the 3GPP specifications, confirms that our model provides an accurate estimation of the system outage event and the number of supported MTC devices.

Device-to-Device communications are expected to play an important role in current and future cellular generations, by increasing the spatial reuse of spectrum resources and enabling lower latency communication links. This paradigm has two fundamental building blocks: (i) proximity discovery and (ii) direct communication between proximate devices. While (ii) is treated extensively in the recent literature, (i) has received relatively little attention. In this paper we analyze a network-assisted underlay proximity discovery protocol, where a cellular device can take the role of: announcer (which announces its interest in establishing a D2D connection) or monitor (which listens for the transmissions from the announcers). Traditionally, the announcers transmit their messages over dedicated channel resources. In contrast, inspired by recent advances on receivers with multiuser decoding capabilities, we consider the case where the announcers underlay their messages in the downlink transmissions that are directed towards the monitoring devices. We propose a power control scheme applied to the downlink transmission, which copes with the underlay transmission via additional power expenditure, while guaranteeing both reliable downlink transmissions and underlay proximity discovery.

The need to carry out analytical studies of wireless systems often motivates the usage of simplified models which, despite their tractability, can easily lead to an overestimation of the achievable performance. In the case of dense small cells networks, the standard single slope path-loss model has been shown to provide interesting, but supposedly too optimistic, properties such as the invariance of the outage/coverage probability and of the spectral efficiency to the base station density. This paper seeks to explore the performance of dense small cells networks when a more accurate path-loss model is taken into account. We first propose a stochastic geometry based framework for small cell networks where the signal propagation accounts for both the Line-of-Sight (LOS) and Non-Line-Of-Sight (NLOS) components, such as the model provided by the 3GPP for evaluation of pico-cells in Heterogeneous Networks. We then study the performance of these networks and we show the dependency of some metrics such as the outage/coverage probability, the spectral efficiency and Area Spectral Efficiency (ASE) on the base station density and on the LOS likelihood of the propagation environment. Specifically, we show that, with LOS/NLOS propagation, dense networks still achieve large ASE gain but, at the same time, suffer from high outage probability.

Machine-to-Machine (M2M) communications are one of the major drivers of the cellular network evolution towards 5G systems. One of the key challenges is on how to provide reliability guarantees to each accessing device in a situation in which there is a massive number of almost-simultaneous arrivals from a large set of M2M devices. The existing solutions take a reactive approach in dealing with massive arrivals, such as non-selective barring when a massive arrival event occurs, which implies that the devices cannot get individual reliability guarantees. In this paper we propose a proactive approach, based on a standard operation of the cellular access. The access procedure is divided into two phases, an estimation phase and a serving phase. In the estimation phase the number of arrivals is estimated and this information is used to tune the amount of resources allocated in the serving phase. Our results show that the proactive approach is instrumental in delivering high access reliability to the M2M devices.

Machine-to-Machine (M2M) communications is one of the key enablers of the Internet of Things (IoT). Billions of devices are expected to be deployed in the near future for novel M2M applications demanding ubiquitous access and global connectivity. In order to cope with the massive number of machines, there is a need for new techniques to coordinate the access and allocate the resources. Although the majority of the proposed solutions are focused on the adaptation of the traditional cellular networks to the M2M traffic patterns, novel approaches based on the direct communication among nearby devices may represent an effective way to avoid access congestion and cell overload. In this paper, we propose a new strategy inspired by the classical Trunked Radio Systems (TRS), exploiting the Device-to-Device (D2D) connectivity between cellular users and Machine-Type Devices (MTDs). The aggregation of the locally generated packets is performed by a user device, which aggregates the machine-type data, supplements it with its own data and transmits all of them to the Base Station. We observe a fundamental trade-off between latency and the transmit power needed to deliver the aggregate traffic, in a sense that lower latency requires increase in the transmit power.

Two of the emerging trends in wireless cellular systems are device-to-device (D2D) and machine-to-machine (M2M) communications. D2D enables efficient reuse of the licensed spectrum to support localized transmissions, while M2M connections are often characterized by fixed and low transmission rates. D2D connections can be instrumental in localized aggregation of uplink M2M traffic to a more capable cellular device, before being finally delivered to the base station (BS). In this paper we show that a fixed M2M rate is an enabler of efficient machine-type D2D underlay operation taking place simultaneously with another downlink cellular transmission. In the considered scenario, aBS B transmits to a user U, while there are NMmachine-type devices (MTDs) attached to U, all sending simultaneously to U and each using the same rate RM. While assuming that B knows the channel B - U, but not the interfering channels from the MTDs to U, we prove that there is a positive downlink rate that can always be decoded by U, leading to zero-outage of the downlink signal. This is a rather surprising consequence of the features of the multiple access channel and the fixed rate RM. We also consider the case of a simpler, single-user decoder at U with successive interference cancellation. However, with single-user decoder, a positive zero-outage rate exists only when NM= 1 and is zero when NM> 1. This implies that joint decoding is instrumental in enabling fixed-rate underlay operation.

We propose a contention-based random-access protocol, designed for wireless networks where the number of users is not a priori known. The protocol operates in rounds divided into equal-duration slots, performing at the same time estimation of the number of users and resolution of their transmissions. The users independently access the wireless link on a slot basis with a predefined probability, resulting in a distribution of user transmissions over slots, based on which the estimation and contention resolution are performed. Specifically, the contention resolution is performed using successive interference cancellation which, coupled with the use of the optimized access probabilities, enables throughputs that are substantially higher than the traditional slotted ALOHA-like protocols. The key feature of the proposed protocol is that the round durations are not a priori set and they are terminated when the estimation/contention-resolution performance reach the satisfactory levels.

The International Telecommunication Union (ITU) established new requirements for the next generation of wireless communications. To meet those requirements, the concept of femtocells emerged as a solution, aiming at increasing capacity and offloading the macrocell network. In a co-channel deployment between macrocells and femtocells, the interference is a serious problem and that needs to be addressed. Since the femtocells are deployed by the end-user, the operator does not have a pre-planned solution to avoid interference, thus a self-organizing solution between femtocells located in the same area is required to manage the interference. In this paper we propose a flexible spectrum usage algorithm which runs at the femtocells, while the macrocells use a fixed reuse scheme in order to manage the interference in the network. In this study we verify that by assigning a fixed reuse scheme 1/3 for the macrocells, the performance achieved by the users is higher, when comparing the same scenario with reuse 1. We also propose a flexible spectrum usage algorithm for the femto cell, which is able to achieve higher user throughput in the femto layer and minimize the interference in the macro layer, when compared to a non-channel aware algorithm, which allocates the PRBs randomly.

Disaster relief networks have to be highly adaptable and resilient. Cognitive radio enhanced ad-hoc architecture have been put forward as a candidate to enable such networks. Spectrum sensing is the cornerstone of the cognitive radio paradigm, and it has been the target of intensive research. The main common conclusion was that the achievable spectrum sensing accuracy can be greatly enhanced through the use of cooperative sensing schemes. When considering applying Cognitive Radio to ad-hoc disaster relief networks, spectrum sensing cooperative schemes are paramount. A centralized cluster-based orchestration cooperative sensing scheme is proposed, where the cluster head controls and adapts the distribution of the cluster sensing's nodes according to the monitored spectrum state. The proposed scheme performance is evaluated through a framework, which allows gauging the accuracy of wideband multi-channel spectrum sensing cooperative schemes, showing that the proposed scheme performance reaches the theoretical maximum achievable accuracy while outperforming the round robin scheme.

Disaster relief networks need to be highly adaptable and resilient in order to encompass the emergency service demands. Cognitive Radio enhanced ad-hoc architecture have been put forward as candidate to enable such networks. Spectrum sensing, the cornerstone of the Cognitive Radio paradigm, has been the target of intensive research, of which the main common conclusion was that the achievable spectrum sensing accuracy can be greatly enhanced through the use of cooperative sensing schemes. When considering applying Cognitive Radio to ad-hoc disaster relief networks, the use of spectrum sensing cooperative schemes becomes essential. A cluster based decentralized orchestration cooperative sensing scheme is proposed, where each node in the cluster decides which spectrum it should monitor, according to the past sensing decisions of all the cluster nodes. The proposed scheme performance is evaluated through a framework, which allows gauging the accuracy of multi narrow-band spectrum sensing cooperative schemes as well as to gauge the error in the estimation of each of the channels un-occupancy. Through that evaluation it is shown that the proposed decentralized scheme performance reaches the performance of the correspondent centralized scheme while outperforming the Round Robin scheme.

The trend on the proliferation of handheld devices triggered an increase on the development of pervasive and personalized mobile applications that exploit and support peer-to-peer/ad-hoc networks. This creates the conditions and motivation for a mobile electronic ID system, preferably one which provides a friendly privacy solution. The existing mobile identification solutions place the interviewer in a more authoritative position than the interviewee, while little or no privacy control is applied by the interviewee. With the mobile ID system (MobIS), this paper proposes a universal mobile ID system which is suitable for various scenarios (e.g. for professional, medical, or official uses) in a heterogeneous network environment. Such systems are highly prone to security and privacy threats, so a context aware privacy mechanism is developed in the proposed framework. The security and privacy frameworks are elaborated, and a demonstration of the prototype is presented in this paper.

The UMTS common transport channels forward access channel (FACH) and the random access channel (RACH) are two of the three fundamental channels for a functional implementation of an UMTS network. Most signaling procedures, such as the registration procedure, make use of these channels and as such it is necessary that both channels be available across the cell radius. This requirement makes the choice of the transmission parameters a fundamental one. This paper presents a sensitivity analysis regarding the transmission parameters of two UMTS common channels: RACH and FACH. Optimization of these channels is performed and values for the key transmission parameters in both common channels are obtained. On RACH these parameters are the message to preamble offset, the initial SIR target and the preamble power step while on FACH it is the transmission power offset.